POLYETHYLENE
ENCASEMENT
Effective, Economical Protection
for Ductile Iron Pipe
In Corrosive Environments
®
Introduction
I
N MORE THAN 40 years of service
in thousands of utilities in the United
States and throughout the world,
polyethylene encasement has proved
an effective corrosion-protection system
for millions of feet of Cast and Ductile
Iron pipe. Today, it is the most widely
used method of protecting Ductile Iron
pipe installed in corrosive environments.
Polyethylene encasement involves
simply wrapping the pipe with a tube or
sheet of polyethylene immediately before
installing the pipe. It is easy for construction
crews to install on-site and is by far the most
economical way to protect Ductile Iron pipe.
And, unlike cathodic protection systems and bonded coatings, polyethylene
encasement is a passive protection
system, so it requires no monitoring,
maintenance, or supervision once installed.
This brochure will briefly present the
history and development of polyethylene
encasement, explain how it protects
Ductile Iron pipe, and highlight field
investigations across the nation. It will also
discuss polyethylene’s advantages over
other corrosion-protection methods,
explain how to ascertain if protection is
warranted outline proper installation
procedures and briefly review cost
considerations when choosing a corrosionprotection system for Ductile Iron pipe.
History and Development
Polyethylene encasement was first used
experimentally in 1951 by the Cast Iron
Pipe Research Association (CIPRA)* and
one of its member companies to protect a
mechanical joint pipe assembly in a highly
corrosive cinder fill in Birmingham,
Alabama. When examined two years later,
the unprotected parts of the pipe showed
significant pitting due to corrosion. The
glands, nuts, bolts, and portion of the pipe
protected by polyethylene encasement
were in excellent condition.
* The Cast Iron Pipe Research Association
(CIPRA) became the Ductile Iron Pipe Research
Association (DIPRA) in 1979.
Although most soil environments are not
considered corrosive to Ductile Iron pipe,
soils in landfill sites such as the one
pictured here are generally considered
corrosive. Other typically corrosive
environments include swamps, peat
bogs, expansive clays, and alkali soils.
2
Chuck Seal
POLYETHYLENE ENCASEMENT
Also in the early 1950s, CIPRA began an
ongoing testing program, burying bare and
polyethylene-encased Cast Iron pipe
specimens in highly corrosive muck in the
Florida Everglades and later in a tidal salt
marsh in Atlantic City, New Jersey.
The success of these early installations
led to the development of an extensive,
ongoing research program that determined
polyethylene encasement’s efficacy in
providing a high degree of corrosion
protection for Cast and Ductile Iron pipe in
most soil environments.
By the late 1950s, successful results in
CIPRA’s research program led to the first
use of polyethylene encasement in operating water systems in Lafourche Parish,
Louisiana, and Philadelphia, Pennsylvania.
And, in 1963, CIPRA continued its research
with the burial of the first polyethyleneencased Ductile Iron pipe specimens in test
sites in the Everglades and Wisconsin
Rapids, Wisconsin. Millions of feet of
polyethylene-encased Cast and Ductile Iron
pipe have since been installed in thousands
of operating water systems across the
United States and throughout the world.
Due to polyethylene encasement’s
excellent success in actual field conditions,
the first national standard, ANSI/AWWA
C105/A21.5, was adopted in 1972. The
American Society for Testing and Materials
issued a standard for polyethylene (ASTM
A674) in 1974. In 1981, Great Britain adopted
a national standard. National and industry
standards in several other countries followed.
An international standard for polyethylene
sleeving (ISO 8180) was adopted in 1985.
The material requirement called for in
AWWA C105 Standard when it was issued
in 1972 was 8-mil, low-density (LD)
polyethylene. With the 1993 revision to
this standard, the section on materials was
expanded to include 4-mil, high-density,
cross-laminated (HDCL) polyethylene.
HDCL polyethylene was first installed
on an operating pipeline in Aurora, Colorado,
in 1981. In 1982, DIPRA began investigating
the corrosion protection afforded Ductile
Iron pipe by 4-mil HDCL polyethylene
encasement at its Logandale, Nevada, test
site. During the 1993 revision of AWWA
C105, the A21 Committee reviewed the test
data on 4-mil HDCL polyethylene and
concluded that from all indications, it provides
comparable protection of Ductile Iron pipe to
that afforded by the standard 8-mil LD
polyethylene. Based on that conclusion, the
A21 Committee elected to incorporate the
4-mil HDCL polyethylene into the standard.
With the 1993 revision of the standard,
the section on materials was also updated
to include Class B (colored) polyethylene
to allow for color coding of potable/reclaimed/
wastewater pipelines as required by many
local/state regulatory agencies.
The 1999 revision of AWWA C105
included: (1) the deletion of 8-mil LD
polyethylene film, (2) the addition of 8-mil
linear low-density (LLD) polyethylene film,
and (3) the addition of impact, tear-resistant
and marking requirements for both
materials (LLD and HDCL). The revision
benefitted the user by reflecting an
improved polyethylene material.
Since the standard was first published in
1972, the polyethylene film industry has
made a number of technological advances.
The LD film, which continues to serve the
industry well, had become more difficult to
obtain. Newer materials, such as LLD film,
which replaced the LD film, are readily
available, much stronger, and more
resistant to damage. The material
requirements for the LLD film were
closely patterned after the Australian
Standard for Polyethylene Sleeving for
Ductile Iron Pipelines (AS 3680) where the
material has been in use for several years.
Laboratory tests indicate that the 4-mil
HDCL and the 8-mil LLD polyethylene
may be more resistant to construction
damage than the old 8-mil LD polyethylene.
Tensile strength, impact strength and
puncture resistance of the 4-mil HDCL and
the 8-mil LLD polyethylene are typically
greater because of inherent differences in
the materials. Based on DIPRA’s laboratory
and field research, either the 8-mil LLD or
the 4-mil HDCL polyethylene materials is
recommended in accordance with AWWA
C105 Standard for corrosion protection of
Ductile Iron pipe in aggresive environments.
Standards for
Polyethylene
Encasement
ANSI/AWWA C105/A21.5
United States
ASTM A674
United States
JDPA Z 2005
Japan
BS6076
Great Britain
ISO 8180
International
DIN 30 674, Part 5
Republic of Germany
A.S. 3680 and A.S. 3681
Australia
1972
1974
1975
1981
1985
1985
1989
3
As with any corrosion-protection
system, proper installation is important
to polyethylene encasement’s success.
Polyethylene encasement should be
carefully installed following one of
three installation methods outlined in
ANSI/AWWA C105/A21.5.
How Polyethylene
Encasement Protects
Ductile Iron Pipe
At the trench, crew members encase
Ductile Iron pipe with a tube or sheet of
polyethylene immediately before installing
the pipe. The polyethylene acts as an
unbonded film, which prevents direct
contact of the pipe with the corrosive soil. It
also effectively reduces the electrolyte
available to support corrosion activity to any
moisture that might be present in the thin
annular space between the pipe and the
polyethylene film.
Typically, some groundwater will seep
beneath the wrap. Although the entrapped
water initially has the corrosive characteristics of the surrounding soil, the available
dissolved oxygen supply beneath the wrap is
soon depleted and the oxidation process
stops long before any damage occurs. The
water enters a state of stagnant equilibrium,
and a uniform environment exists around
the pipe.
The polyethylene film also retards the
diffusion of additional dissolved oxygen to
the pipe surface and the migration of corrosion products away from the pipe surface.
Polyethylene encasement is not designed
to be a watertight system. Yet, once
installed, the weight of the earth backfill and
surrounding soil prevents any significant
exchange of groundwater between the wrap
and the pipe.
Advantages of
Polyethylene Encasement
Although there are other ways to protect
Ductile Iron pipe in corrosive environments,
including cathodic protection and special
external bonded coatings, no method has
proved both as effective and economical as
polyethylene encasement.
Polyethylene’s excellent dielectric properties enable it to effectively shield the pipe
from low-level stray direct current. And,
because polyethylene provides a uniform
4
environment for the pipe, local galvanic
corrosion cells are virtually eliminated.
Pinholes in the loose wrapping
material do not significantly diminish its
protective ability. And, unlike bonded
coatings, polyethylene has the ability to
protect the pipe without the formation of
concentration cells at coating holidays.
Polyethylene encasement is easy to
install and requires no additional manpower
or special equipment. Construction crew
members simply slip the polyethylene over
the pipe as they install it.
Compared to cathodic protection and
bonded coatings, polyethylene encasement is very inexpensive. The initial cost
of material and installation is very low —
only pennies per foot in most sizes. In
fact, many utilities that install their own
pipe assign no installation cost for the
encasement, reporting that the material
costs as little as a few cents per inchdiameter per foot.
Polyethylene encasement is fieldapplied, so the pipe doesn’t require special
handling or packaging during shipment.
And, because installation is on site, damage
is less likely than on factory-applied
coatings. If damaged, the polyethylene is
easy and simple to repair at the job site with
polyethylene compatible adhesive tape.
Chuck Seal
Because polyethylene is a passive
sys tem of protection, it requires no
expensive maintenance or monitoring
and costs nothing to operate once
installed.
Polyethylene
Encasement
• Is inexpensive.
• Is easy to install.
• Requires no additional manpower.
• Requires no maintenance or
monitoring.
• Costs nothing to operate.
• Doesn’t deteriorate underground.
• Is easily repaired with polyethylene
adhesive tape if damaged.
• Doesn’t require any special handling
or packaging during shipment.
• Provides a uniform environment
for the pipe, virtually eliminating
galvanic corrosion cells.
• Protects the pipe without the
formation of concentration cells at
coating holidays.
How to Identify
Corrosive Environments
It is important to identify potentially
corrosive environments prior to pipeline
installation because, once a pipeline is
installed, it is both costly and difficult to
retrofit with corrosion protection
measures.
Although Ductile Iron pipe possesses
good resistance to corrosion and needs no
additional protection in most soils,
experience has shown that external
corrosion protection is warranted in certain
soil environments. Examples include soils
with low resistivities, anaerobic bacteria,
differences in composition, and differential
aeration around the pipe. Dissimilar metals
and external stray direct currents may also
necessitate additional corrosion protection.
Soils contaminated by coal mine
wastes, cinders, refuse, or salts also are
generally considered corrosive. So are
certain naturally occurring environ ments, such as swamps, peat bogs,
expansive clays, and alkali soils. And
soils in wet, low-lying areas are generally
considered more corrosive than those in
well-drained areas.
10-Point Soil Evaluation
Procedure
Although several evaluation procedures
have been used to predict conditions
corrosive to underground piping, the 10point soil evaluation procedure instituted
by CIPRA in 1964 is most often
recommended for Ductile Iron pipe.
Included in the Appendix to the
ANSI/AWWA C105/A21.5 Standard, the
10-point system has proved invaluable in
surveying more than 100 million feet of
proposed pipeline installations to
determine soil corrosivity.
The evaluation procedure is based
upon information drawn from five tests
and observations:
• Soil resistivity
• pH
• Oxidation-reduction (redox)
potential
• Sulfides
• Moisture
For a given soil sample, each parameter
is evaluated and assigned points according
to its contribution to corrosivity. The
points for all five areas are totaled, and if
the sum is 10 or more, the soil is
considered corrosive to Ductile Iron pipe,
and protective measures should be taken.
In addition, potential for stray direct
current corrosion should also be
considered as part of the evaluation. Notes
on previous experience with underground
structures in the area are also very
important in predicting soil corrosivity.
It is important to note that the 10-point
system, like any evaluation procedure, is
intended as a guide in determining a soil’s
potential to corrode Ductile Iron pipe. It
should be used only by qualified engineers
or technicians experienced in soil analysis
and evaluation.
Soil Test Evaluation for
Ductile Iron Pipe
(10-Point System)*
Soil Characteristics
Resistivity (ohm-cm)**
<1,500
>1,500-1,800
>1,800-2,100
>2,100-2,500
>2,500-3,000
>3,000
pH
0-2
2-4
4-6.5
6.5-7.5
7.5-8.5
>8.5
Redox potential
>+100 mv
+50 to +100 mv
0 to +50 mv
Negative
Sulfides
Positive
Trace
Negative
Points
10
8
5
2
1
0
5
3
0
0 ***
0
3
0
3.5
4
5
3.5
2
0
Moisture
Poor drainage,
continuously wet
Fair drainage,
generally moist
Good drainage,
generally dry
2
1
0
*** Ten points–corrosive to Ductile Iron pipe.
Protection is indicated.
*** Based on water-saturated soil box. This
method is designed to obtain the lowest–and
most accurate–resistivity reading.
*** If sulfides are present and low (<100 mv)
or negative redox-potential results are
obtained, 3 points should be given for
this range.
Note: DIPRA recommends that the soil sample
used in the 10-point evaluation be taken at pipe
depth rather than at the surface. Soil corrosivity
readings can vary substantially from the
surface to pipe depth.
5
POLYETHYLENE ENCASEMENT
Merritt Island, FL
27 years
24-inch Cast Iron pipe encased in loose
8-mil polyethylene
Installed 1963. Inspected 1990.
Soil Analysis:
Description: gray and black loamy
sand
Resistivity: 1,120 ohm-cm (10)*
pH: 7.1 (3)
Redox: -20 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (23.5)
Condition of Pipe and Encasement:
excellent
Waterford, MI
20 years
Philadelphia, PA
30 years
8-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1975. Inspected 1995.
Soil Analysis:
Description: black and gray silty clay
Resistivity: 960 ohm-cm (10)
pH: 7.5 (3)
Redox: +23 mv (3.5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (22)
Condition of Pipe and Encasement:
excellent
12-inch Cast Iron pipe encased in loose
8-mil polyethylene
Installed 1959. Inspected 1989.
Soil Analysis:
Description: landfill area–brownish red
clayey silts and dark gray organic
clays with organic materials and
petroleum and paper wastes
Resistivity: 2,400 to 5,600 ohm-cm (2)
pH: 3.9 to 6.2 (3)
Redox: +67 to +69 mv (3.5)
Sulfides: positive (3.5)
Moisture: moist to saturated (2)
Soil Condition: corrosive (14)
Condition of Pipe and Encasement:
very good
*Numbers in parentheses indicate point count per Soil Test Evaluation procedure outlined in Appendix A of ANSI/AWWA C105/A21.5. See table on page 5 of this brochure
for explanation.
Ogden, UT
10 years
Mitchell, SD
18 years
Detroit, MI
21 years
16-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1979. Inspected 1989.
Soil Analysis:
Description: dark gray silty clay
Resistivity: 192 ohm-cm (10)
pH: 7.9 (0)
Redox: -165 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (20.5)
Condition of Pipe and Encasement:
excellent
12-inch Cast Iron pipe encased in loose
8-mil polyethylene
Installed 1963. Inspected 1981.
Soil Analysis:
Description: brown clay and sand with
cinders present
Resistivity: 840 ohm-cm (10)
pH: 7.1 (0)
Redox: +450 mv (0)
Sulfides: trace (2)
Moisture: moist (1)
Soil Condition: corrosive (13)
Condition of Pipe and Encasement:
excellent
8-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1974. Inspected 1995.
Soil Analysis:
Description: gray and black silty clay
Resistivity: 1,320 ohm-cm (10)
pH: 7.4 (3)
Redox: -113 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (23.5)
Condition of Pipe and Encasement:
excellent
6
INVESTIGATIONS
Omaha, NE
15 years
12-inch Cast Iron pipe encased in loose
8-mil polyethylene
Installed 1974. Inspected 1989.
Soil Analysis:
Description: gray clay
Resistivity: 600 ohm-cm (10)*
pH: 7.4 (3)
Redox: +90 mv (3.5)
Sulfides: positive (3.5)
Moisture: wet (2)
Soil Condition: corrosive (22)
Condition of Pipe and Encasement:
excellent
Charleston, SC
21 years
Syracuse, NY
15 years
24-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1967. Inspected 1988.
Soil Analysis:
Description: gray sand and clay with
organic muck in reclaimed marsh
subjected to fluctuating water table
due to coastal tidal effect
Resistivity: 560 ohm-cm (10)
pH: 6.9 (3)
Redox: -132 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (23.5)
Condition of Pipe and Encasement:
excellent
8-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1988. Inspected 2003.
Soil Analysis:
Description: dark, organic brown clay
Resistivity: 410 ohm-cm (10)
pH: 6.9 (3)
Redox: -40 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (23.5)
Condition of Pipe and Encasement:
excellent
*Numbers in parentheses indicate point count per Soil Test Evaluation procedure outlined in Appendix A of ANSI/AWWA C105/A21.5. See table on page 5 of this brochure
for explanation.
Fayetteville, AR
30 years
12-inch Gray Iron pipe encased in loose
8-mil polyethylene
Installed 1973. Inspected 2003.
Soil Analysis:
Description: dark gray clay
Resistivity: 1,600 ohm-cm (8)
pH: 6.8 (3)
Redox: -100 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (21.5)
Condition of Pipe and Encasement:
excellent
Jackson, MS
9 years
Little Rock, AR
14 years
8-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1977. Inspected 1986.
Soil Analysis:
Description: mixture of organic clay
and brown silty clay
Resistivity: 880 ohm-cm (10)
pH: 4.4 (0)
Redox: -150 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (20.5)
Condition of Pipe and Encasement:
excellent
30-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1972. Inspected 1986.
Soil Analysis:
Description: dark reddish and grayish
brown clay
Resistivity: 600 ohm-cm (10)
pH: 6.9 (3)
Redox: +40 mv (4)
Sulfides: trace (2)
Moisture: saturated (2)
Soil Condition: corrosive (21)
Condition of Pipe and Encasement:
excellent
7
Montgomery, AL
20 years
36-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1982. Inspected 2002.
Soil Analysis:
Description: reddish brown clayey
sand
Resistivity: 172 ohm-cm (10)*
pH: 8.7 (3)
Redox: +30 mv (4)
Sulfides: negative (0)
Moisture: saturated (2)
Soil Condition: corrosive (19)
Condition of Pipe and Encasement:
excellent
Lafourche Parish, LA
40 years
4-inch Cast Iron pipe encased in loose
8-mil polyethylene
Installed 1958. Inspected 1998.
Soil Analysis:
Description: gray clay with black
organics
Resistivity: 520 ohm-cm (10)
pH: 6.3 (0)
Redox: -50 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (20.5)
Condition of Pipe and Encasement:
excellent
Latham, NY
36 years
6-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1962. Inspected 1998.
Soil Analysis:
Description: dark brown stiff clay
Resistivity: 600 ohm-cm (10)
pH: 7.1 (0)
Redox: +200 mv (0)
Sulfides: negative (XX)
Moisture: saturated (2)
Soil Condition: corrosive (12)
Condition of Pipe and Encasement:
excellent
*Numbers in parentheses indicate point count per Soil Test Evaluation procedure outlined in Appendix A of ANSI/AWWA C105/A21.5. See table on page 5 of this brochure
for explanation.
St. George, UT
16 years
12-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1968. Inspected 1984.
Soil Analysis:
Description: dark gray clayey silt
Resistivity: 720 ohm-cm (10)
pH: 7.3 (0)
Redox: +110 mv (0)
Sulfides: negative (0)
Moisture: saturated (2)
Soil Condition: corrosive (12)
Condition of Pipe and Encasement:
excellent
8
City of Orange, CA
18 years
6-inch Cast Iron pipe encased in loose
8-mil polyethylene
Installed 1969. Inspected 1987.
Soil Analysis:
Description: brown silty clay
Resistivity: 640 ohm-cm (10)
pH: 6.3 (0)
Redox: +170 mv (0)
Sulfides: negative (0)
Moisture: saturated (2)
Soil Condition: corrosive (12)
Condition of Pipe and Encasement:
excellent
St. Louis, MO
13 years
12-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1973. Inspected 1986.
Soil Analysis:
Description: sticky gray-brown clay
Resistivity: 600 ohm-cm (10)
pH: 6.7 (0)
Redox: +150 mv (0)
Sulfides: negative (0)
Moisture: moist (1)
Soil Condition: corrosive (11)
Condition of Pipe and Encasement:
excellent
Additional Polyethylene
Encasement Investigations
Nanticoke, ON, Canada
16 years
16-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1977. Inspected 1993.
Soil Analysis:
Description: brown, gray, and black
silty clay
Resistivity: 960 ohm-cm (10)
pH: 7.3 (3)
Redox: -18 mv (5)
Sulfides: positive (3.5)
Moisture: saturated (2)
Soil Condition: corrosive (23.5)
Condition of Pipe and Encasement:
very good
Farmington/
Shiprock, NM
20 years
16-inch Ductile Iron pipe encased in loose
8-mil polyethylene
Installed 1968. Inspected 1988.
Soil Analysis:
Description: light brown clayey silt
with some gravel and rock
Resistivity: 400 ohm-cm (10)
pH: 7.7 (0)
Redox: +146 mv (0)
Sulfides: trace (2)
Moisture: saturated (2)
Soil Condition: corrosive (14)
Condition of Pipe and Encasement:
excellent
9
ANSI/AWWA C105/A21.5
Installation Methods
Proper Installation of
Polyethylene Encasement
As with any corrosion-protection system,
proper installation is important to
polyethylene encasement’s success. Care
taken during installation is as important as
the installation method itself. The few
known failures of polyethylene-encased
Cast and Ductile Iron pipe have generally
been due to improper installation or poor
workmanship.
The ANSI/AWWA C105/A21.5 Standard
outlines three methods of installing
polyethylene sleeving. Methods A and B
use polyethylene tubes, and Method C
uses polyethylene sheets.
Method A uses one length of polyethylene tube, overlapped at the joints, for
each length of pipe. Because installation is
faster and easier, most utilities and contractors choose some form of Method A.
Method B uses a length of polyethylene
tube for the barrel of the pipe and a
separate length of polyethylene tube or
sheet for the joints. The national standard
does not recommend Method B for bolted-type
joints unless an additional layer of
polyethylene is provided over the joint area as
in Methods A and C.
In Method C, each section of pipe is
completely wrapped with a flat polyethylene sheet.
Method A
In this method, which is preferred by most utilities and contractors, one length of polyethylene tube, overlapped at the joints,
is used for each length of pipe.
Method B
A length of polyethylene tube is used for the barrel of the pipe
and separate lengths of polyethylene tube or sheets are used for
the joints. Note: Method B is not recommended for bolted-type
joints unless an additional layer of polyethylene is provided over
the joint area as in Methods A and C.
Method C
Each section of pipe is completely wrapped with a flat
polyethylene sheet.
10
Method A
for Normal Dry Trench Conditions
Step 1.
Cut a section of polyethylene tube approximately two feet longer
Step 5.
than the pipe section. Remove all lumps of clay, mud, cinders, or
Overlap the secured tube end with the tube end of the new pipe
other material that might have accumulated on the pipe surface
section. Secure the new tube end in place.
during storage. Slip the polyethylene tube around the pipe,
starting at the spigot end. Bunch the tube accordion-fashion on
the end of the pipe. Pull back the overhanging end of the tube
until it clears the pipe end.
Step 6.
Take up slack in the tube along the barrel of the pipe to make a
snug, but not tight, fit. Fold excess polyethylene back over the
top of the pipe.
Step 2.
Dig a shallow bell hole in the trench bottom at the joint location
to facilitate installation of the polyethylene tube. Lower the pipe
into the trench and make up the pipe joint with the preceding
section of pipe.
Step 7.
Secure the fold at several locations along the pipe barrel
(approximately every three feet).
Step 3.
Move the cable to the bell end of the pipe and lift the pipe
slightly to provide enough clearance to easily slide the tube.
Spread the tube over the entire barrel of the pipe. Note: Make
sure that no dirt or other bedding material becomes trapped
between the wrap and the pipe.
Step 4.
Make the overlap of the polyethylene tube by pulling back the
bunched polyethylene from the preceding length of pipe and
securing it in place. Note: The polyethylene may be secured in
place by using tape, string, plastic tie straps, or any other
material capable of holding the polyethylene encasement snugly
against the pipe.
Step 8.
Repair all small rips, tears, or other tube damage with adhesive
tape. If the polyethylene is badly damaged, repair the damaged
area with a sheet of polyethylene and seal the edges of the repair
with adhesive tape.
Step 9.
Carefully backfill the pipe according to the AWWA C600 standard
for backfill procedure. To prevent damage during backfilling, allow
adequate slack in the tube at the joint. Backfill should be free of
cinders, rocks, boulders, nails, sticks, or other materials that
might damage the polyethylene. Avoid damaging the polyethylene
when using tamping devices.
11
Alternate Method A
for Wet Trench Conditions
In wet, sloppy trench conditions, the pipe should be completely
covered by the polyethylene tube before it is lowered into the
trench. This alternate method is illustrated below.
Step 1.
Cut the polyethylene tube to a length approximately two feet
longer than that of the pipe section. Slip the tube over the pipe.
Step 2.
Spread the tube over the entire barrel of the pipe, pushing back
both ends of the tube until they clear both pipe ends. Make sure
the tube is centered on the pipe to provide a one-foot overlap at
each end.
Step 3.
Take up slack in the tube to make a snug, but not tight, fit. (See
previous page.) Circumferential wraps of tape or plastic tie straps
should be placed at 2-foot intervals along the barrel of the pipe to
help minimize the space between the polyethylene and the pipe.
Wrap a piece of tape or plastic tie strap completely around the
pipe at each end to seal the polyethylene, leaving ends free to
overlap the adjoining sections of pipe.
Step 4.
Lower pipe into the trench and make up the pipe joint. Be careful
not to damage the polyethylene when handling or jointing the
pipe. Complete the installation following dry condition Steps 4, 5
(taking care to seal ends of overlap by wrapping tape or plastic tie
straps completely around the pipe at each end), 8, and 9 on
previous page. Note: When lifting polyethylene-encased pipe, use
a fabric-type sling or a suitably padded cable or chain to prevent
damage to the polyethylene.
If you have any problems or questions about installing
polyethylene encasement, contact DIPRA or one of its member
companies.
12
Appurtenances
Pipe-shaped appurtenances
Cover bends, reducers, offsets, and other
pipe-shaped appurtenances in the same
manner as the pipe.
Odd-shaped appurtenances
Wrap odd-shaped appurtenances such as
valves, tees, and crosses with a flat sheet or
split length of polyethylene tube by passing
the sheet under and then over the
appurtenance and bringing it together
around the body of the appurtenance. Make
seams by bringing the edges of the
polyethylene together, folding over twice,
and taping them down.
Joints
Overlap joints as in normal installation;
then tape the polyethylene securely in
place at valve stems and other penetrations.
When bolted-type joints are used, care
should always be taken to prevent bolts or
other sharp edges of the joint configuration
from penetrating the wrap.
Branches, blowoffs, air valves
To provide openings for branches, blowoffs, air valves, and similar appurtenances,
make an X-shaped cut in the polyethylene
and temporarily fold back the film. After
installing the appurtenance, tape the slack
securely to the appurtenance and repair the
cut and any other damaged areas in the
polyethylene with tape.
Service taps
The preferred method of tapping
polyethylene-encased Ductile Iron pipe
involves wrapping two or three layers of
polyethylene adhesive tape completely
around the pipe to cover the area where the
tapping machine and chain will be mounted.
Then install the corporation stop directly
through the tape and polyethylene. After
the tap is made inspect the entire
circumferential area for damage and make
any necessary repairs.
Recommended Tapping
Method
To perform the preferred method of
tapping polyethylene-encased Ductile
Iron pipe, wrap two or three layers of
polyethylene adhesive tape completely
around the pipe to cover the area where
the tapping machine and chain will be
mounted.
Sylvia Caswell
Mount the tapping machine on the pipe
area covered by the polyethylene tape.
Then make the tap and install the
corporation stop directly through the
tape and polyethylene.
Sylvia Caswell
After making the direct service
connection, inspect the entire
circumferential area for damage and
make any necessary repairs.
Sylvia Caswell
13
Randy Usedom
Cost Considerations
Tips for proper installation
1. Quality of installation is more important
than the actual sequence followed.
2. Don’t leave the polyethylene outside in
the sun for long periods before
installation.
3. When lifting polyethylene-encased pipe
with a backhoe, use a fabric-type “sling”
or padded cable to protect the
polyethylene.
4. Be sure to remove all lumps of clay, mud,
cinders, etc., on the pipe surface before
you encase the pipe.
5. Take care to keep soil or bedding material
from becoming trapped between the pipe
and the polyethylene.
6. When installing polyethylene encasement below the water table or in areas
subject to tidal action, seal as thoroughly
as possible both ends of each polyethylene tube with polyethylene adhesive
tape or plastic tie straps at the joint
overlap. Additionally, place circumferential
wraps of tape or plastic tie straps at 2-foot
intervals along the barrel of the pipe to
help minimize the space between the
polyethylene and the pipe.
Polyethylene encasement is more costeffective when compared to alternative
corrosion-control systems like bonded
coatings and cathodic protection.
According to costs outlined in a 1985
U.S. Army Corps of Engineers Technical
Report, installing a 16-mil-thick coating of
coal tar epoxy is five times the cost of
installing polyethylene encasement. And,
this figure doesn’t include the additional
costs of packaging, handling, transportation, and inspection.
Compared to polyethylene encasement, cathodic protection is very expensive to install. According to the same
Corps of Engineers’ report, the cost to
install an impressed-current cathodic
protection system on 12-inch Ductile Iron
pipe is five times the cost of polyethylene
encasement. The cost to install a
sacrificial-anode system is approximately
30 times the cost of polyethylene. These
figures don’t include the ongoing maintenance expense required by both systems,
which, over the life of the systems, are
often much greater than initial design and
installation costs.
Recommended Polyethylene Tube and
Sheet Sizes for Ductile Iron Pipe
Nominal Pipe Diameter
(Inches)
3
4
6
8
10
12
14
16
18
20
24
30
36
42
48
54
60
64
14
Minimum Polyethylene Width (Inches)
Flat tube
Sheet
14
28
14
28
16
32
20
40
24
48
27
54
30
60
34
68
37
74
41
82
54
108
67
134
81
162
81
162
95
190
108
216
108
216
121
242
Conclusion
There is no perfect system of corrosion
protection for buried metallic pipelines.
Failures have been documented with all
types of corrosion-protection systems,
including cathodic protection.
Cathodic protection is very expensive
to install and maintain and can also
damage nearby pipelines through stray
current interference.
Bonded coatings are also expensive.
Plus they can be easily damaged during
shipping, handling, and installation and
are costly and difficult to repair in
the field.
Polyethylene encasement also has
limitations–and it is not universally applicable for all Ductile Iron pipelines where
corrosion protection is warranted. There
are instances where it is not feasible to
install polyethylene encasement due
to unusual construction conditions.
Additionally, in certain high-density stray
current environments and in “uniquely
For more than 40 years, polyethylene
encasement has been used successfully
to protect millions of feet of Cast and
Ductile Iron pipe in a broad range of soil
conditions.
severe environment,” as defined in
Appendix “A” of ANSI/AWWA C105/A21.5,
the sleeving alone might not provide the
degree of protection needed. In such
cases, DIPRA sometimes recommends
alternative methods of corrosion
protection. And, as with all corrosioncontrol methods, the success of
polyethylene encasement is dependent
upon proper installation procedures.
Since the early 1950s, DIPRA has
researched numerous methods of corrosion protection for Gray and Ductile Iron
pipe, including hundreds of investigations
in the laboratory, in field test sites, and
in operating water systems throughout
the United States. New types of polyethylene, various external pipe coatings,
and the use of select backfill have also
been investigated.
More than 40 years of experience have
demonstrated polyethylene encasement’s
effectiveness in protecting Cast and Ductile Iron pipe in a broad range of soil
condi tions. Properly installed poly -
ethylene encasement can effectively
eliminate the vast majority of corrosion
problems encountered by most utilities.
Based on numerous laboratory and
field test results, DIPRA continues to
recommend polyethylene encasement as
the most economical and effective
method of protecting Ductile Iron pipe in
most corrosive environments.
For Further Information
American National Standard for Polyethylene Encasement for Ductile-Iron
Pipe Systems. ANSI/AWWA C105/A21.599. American Water Works Association,
Denver, Colorado.
John C. Anderson, Polyethylene
Encasement for Protection of Ductile Iron
Pipe in Corrosive Environments, Ductile
Iron Pipe Research Association,
Birmingham, Alabama.
A. Michael Horton, “Protecting Pipe
With Polyethylene Encasement,” 1951-
1988, Waterworld News, May/June 1988,
pp. 26-28.
Andrew B. Malizio, “Pipe Digs
Show Ef fect iveness of Poly Sheet
Encasement,” Water Engineering &
Management, October 1986.
Troy F. Stroud, “Corrosion Control
Methods for Ductile Iron Pipe,”
Waterworld News, July/August 1989,
American Water Works Association,
Denver, Colorado.
Troy F. Stroud, “Corrosion Control
Measures For Ductile Iron Pipe,” Paper
No. 585, National Association of
Corrosion Engineers Corrosion 89
Conference, New Orleans, Louisiana,
April 18, 1989.
Troy F. Stroud, “Polyethylene
Encasement versus Cathodic Pro tection: A View on Corrosion
Protection,” Ductile Iron Pipe News,
Spring/Summer 1988, pp. 8-11.
Ernest F. Wagner, “Loose Plastic
Film Wrap as Cast-Iron Pipe
Protection,” Journal American Works
Association Vol. 56, No. 3, March 1964.
T.M. Walski, “Cost of Water
Distribu tion System Infrastructure
Rehabilitation, Repair, and Re placement,” Technical Report EL-85-5.
U.S. Army Corps of Engineers,
Department of the Army, Washington,
D.C., March 1985.
W. Harry Smith, “Corrosion
Prevention with Loose Polyethylene
Encasement,” Water & Sewage Works,
May 1982.
L. Gregg Hor n, “The Design
Decision Model™ For Corrosion
Control of Ductile Iron Pipeling,”
Ductile Iron pipe Research Association,
Birmingham, AL.
15
DIPRA
MEMBER COMPANIES
American Cast Iron Pipe Company
P.O. Box 2727
Birmingham, Alabama 35202-2727
Atlantic States Cast Iron Pipe Company
183 Sitgreaves Street
Phillipsburg, New Jersey 08865-3000
Canada Pipe Company, Ltd.
1757 Burlington Street East
Hamilton, Ontario L8N 3R5 Canada
Clow Water Systems Company
P.O. Box 6001
Coshocton, Ohio 43812-6001
Griffin Pipe Products Co.
1011 Warrenville Road
Lisle, Illinois 60532
McWane Cast Iron Pipe Company
1201 Vanderbilt Road
Birmingham, Alabama 35234
Pacific States Cast Iron Pipe Company
P.O. Box 1219
Provo, Utah 84603-1219
United States Pipe and Foundry Company
P.O. Box 10406
Birmingham, Alabama 35202-0406
®
An association of quality producers dedicated to highest pipe
standards through a program of continuing research.
245 Riverchase Parkway East, Suite O
Birmingham, Alabama 35244-1856
Telephone 205 402-8700 FAX 205 402-8730
http://www.dipra.org
Manufactured from recycled materials.
POLY.TECH/7-02/5M
Published 1-92
Revised 2-12
Copyright © 2000, 1995, 1992 by Ductile Iron Pipe Research Association
This publication, or parts thereof, may not be reproduced in any form without
permission of the publishers.